1. Field of the Invention
The present invention relates to an image forming apparatus of the type using an intermediate image transfer body and more particularly to an image forming apparatus capable of sensing the displacement or shift of an intermediate image transfer body that may occur in a direction perpendicular to the direction of movement of the intermediate image transfer body during operation.
2. Description of the Background Art
A copier, printer or similar image forming apparatus of the type using an intermediate image transfer belt, photoconductive belt, image transfer belt or similar endless belt is conventional. The problem with such an endless belt is that the belt is likely to be shifted or meander in a direction perpendicular to the direction of movement due to the turn thereof. In a color image forming apparatus, for example, any displacement of the endless belt in the above direction causes toner images of different colors to be brought out of register, thereby degrading image quality. In order to solve this problem, a driver for driving the endless belt, particularly one included in a color image forming apparatus, must be configured to adequately control the displacement or the meander of the belt.
Some different methods have heretofore been proposed for controlling the displacement of the above endless belt, as will be described hereinafter. Japanese Patent Laid-Open Publication No. 2002-287527, for example, teaches that by controlling the inclination of an adjust roller, which causes an endless belt passed over it to turn, in proportion to the amount of shift of the belt, it is possible to control the shift with high accuracy. With this scheme, however, it is impossible to determine the amount of shift by taking account of the irregularity of the edge of the belt.
Japanese Patent Laid-Open Publication No. 8-137351 discloses a mechanism adapted for adjusting a position where a drive roller and the edge of an endless belt passed over it contacts each other. This mechanism, however, simply determines whether or not the belt is shifted and cannot execute control in accordance with the amount of shift.
Further, Japanese Patent No. 3,275,627 proposes a belt shift control device using a shift sensing member contacting the widthwise edge of an endless belt for sensing the shift of the belt. The problem with the shift sensing member taught in the above document is that it cannot respond to shifts occurring at fine pitches.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent No. 3,209,451.